the+beginnings+of+life
TRANSCRIPT
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The Beginning of Life
I. Conditions necessary to allow life to begin
Fig. 20-4b, p.321
Earth was a very hostile environment 4 billion years ago
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First Atmosphere
• Hydrogen gas
• Nitrogen
• Carbon monoxide
• Carbon dioxide
• No gaseous oxygen
I. Conditions necessary to allow life to begin
to vacuum pump
CH4NH3H2OH2
gases
electrodes
spark discharge
water out
condenser
water in
water droplets
water containingorganic compounds
liquid water in trap
boiling water
Fig. 20-4c, p.321
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I. Conditions necessary to allow life to begin
four formaldehyde molecules with four pyrrole rings
porphyrin ring system
6H
chlorophyll a
Stepped ArtFig. 20-5, p.322
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Origin of Organic Compounds
• Amino acids, other organic compounds can form spontaneously under conditions like those on early Earth
• Clay may have served as template for complex compounds
• Compounds may have formed near hydrothermal vents
RNA ‘Ribozyme’ produced in the laboratory
Store biological information and also act as catalyst (enzyme)
Could something like this have been the first source of genetic material?
RNA World
• DNA is genetic material now• DNA-to-RNA-to-protein system is complicated• RNA may have been first genetic material• RNA can assemble spontaneously • How switch from RNA to DNA might have
occurred is not known
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II. Origin of cells – precursor to living cells
Proto-Cells
• Microscopic spheres of proteins or lipids can self assemble
• Tiny sacs like cell membranes can form under laboratory conditions that simulate conditions in evaporating tidepools
• Nanobes may resemble proto-cells
Amino acids heated, then moistened.Formed protein membranes.
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II. Origin of cells – precursor to living cells
Fig. 20-7b, p.323
Membrane of fatty acids and alcohol surrounding RNA-coated clay .
II. Origin of cells – precursor to living cells
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Scientists have managed to create "primitive cells" in an experiment which may indicate that life began in space and was delivered to Earth.
Researchers working with the American space agency NASA say their "proto-cells" mimic the membranous structures found in all living things. They were produced in a laboratory experiment that duplicated the harsh conditions of cold interstellar space.
BBC NewsMonday, 29 January, 2001
Could precursors and /or proto-cells have arrived from outer space?
This new work suggests that the early chemical steps believed to be important for the origin of life do not require an already-formed planet.
Instead, they seem to take place in deep space long before planet formation occurs.
This implies that the vastness of space is filled with chemical compounds which, if they land in a hospitable environment like our Earth, can readily jump-start life.
spontaneous formation of lipids,carbohydrates, amino acids, proteins,nucleotides under abiotic conditions
livingcells
self-replicating system enclosed in aselectively permeable, protective lipid sphere
DNA RNA enzymes andother proteins
formation ofprotein-RNA systems,
evolution of DNAformation oflipid spheres
membrane-bound proto-cells
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III. The first true cells
Fig. 20-8a, p.324
3.5 billion y –oldprokaryote
Anaerobic or aerobic?
The First Cells
• Originated in Archeon Eon
• Were prokaryotic heterotrophs
• Secured energy through anaerobic pathways– No oxygen present
– Relied on glycolysis and fermentation
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Stromatolites – fossils of cyanobacteria; 3by-old
Proterozoic Eon
• Origin of photosynthetic Eubacteria
– Cyclic pathway first
– Noncyclic pathway next (cyanobacteria)
• Oxygen accumulates in atmosphere
• Origin of aerobic respiration
Fig. 20-8b, p.324
Eukaryotes2.1 bya
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IV. Where did eukaryotic organelles come from? The evolution of the eukaryotic cell
Where did all these organelles come from?
IV. Where did eukaryotic organelles come from? The evolution of the eukaryotic cell
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DNA
infolding of plasma membraneFig. 20-10a, p.326
ER ?
Possible origin of nucleus
IV. Where did eukaryotic organelles come from? The evolution of the eukaryotic cell
Origin of mitochondria and chloroplasts
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Endosymbiosis example in modern time
Amoeboid organism with green alga within
Evidence
Occurred by phagocytosis
nucleusmitochondrion
photosynthetic organelle thatresembles a cyanobacterium
Evidence
Theory of Endosymbiosis• Lynn Margulis• Mitochondria and chloroplasts are the
descendents of free-living prokaryotic organisms
• Prokaryotes were engulfed by early eukaryotes and became permanent internal symbionts
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V. The timeline of development
hydrogen-rich anaerobic atmosphere atmospheric oxygen, 10%
archaeanlineage
dancestors ofeukaryotes
hendomembrane
system and nucleus
b
origin ofprokaryotes
cyclic pathwayof photosynthesis
e
noncyclic pathwayof photosynthesisf
g aerobic respiration
3.8 billion years ago
3.2 billion years ago
2.5 billion years ago
a
Fig. 20-12b, p.328
atmospheric oxygen, 20%; the ozone layer slowly develops
iendosymbiotic origin
of mitochondira
jorigin of eukaryotes,
the first protists
k origin of animals
jendosymbiotic origin
of chloroplasts
Aerobic species becomes endosymbiot of anaerobic forerunner of eukaryotes.
k origin of fungi
k origin of lineage leading to plants
1.2 billion years ago
900 million years ago
435 million years ago